Actions and events¶
An action is a program, frequently written in a scripting language, which performs a single task. It is typically an encapsulation of a task usually done by a system administrator, such as editing a configuration file or reconfiguring a service. Actions are not called directly; they are always called by signalling an event.
The actions are stored in the
These actions are then linked into the relevant events as the same
action may need to be performed in more than one event.
To create a new action called myaction you simply create a program
to perform the action myaction and save it as
/etc/e-smith/events/actions/myaction . Actions can be written in any
programming language, although additional platform support is provided
for Perl code.
An example action script is:
#!/bin/bash /usr/sbin/lokkit --update
Action script parameters¶
Action scripts are always called with at least one parameter; the name of the current event. Many action scripts can be called with a single additional parameter. This parameter is usually a configuration database key, for example the username being modified. Action scripts rarely require more than two parameters. The details should be stored in the configuration database(s) and only the key should be passed to the action scripts. All configuration details must be stored in the configuration databases and the database key passed as the parameter to the action. This allows other scripts to be added to the event.
Since the system passes the name of the current event as the first parameter, it is often beneficial to write action scripts which are polymorphic based on the event name. For example, the code to create a user and the code to modify an existing user may be only slightly different and may well benefit from being in a single script. Example:
use strict; my $event = $ARGV; my $myarg = $ARGV; exit 0;
Whenever possible, avoid to call events from within action scripts.
Action code libraries¶
To promote code reusability and components abstraction some Perl
modules are available under
/usr/share/perl5/vendor_perl/esmith/. For instance,
Secret generation and persistent storage, under
- Service manager agnostic API. No matter if a service is managed by systemd, Upstart or SysV init script: use this API to gain control over it.
- Access to LDAP, service accounts and ACL management, low-level user and group management.
- Obtain accounts and mail addresses relations. Manage IMAP ACLs.
- Template processing and expansion.
- Event execution and tracking.
For more informations about a specific module, refer its perldoc documentation.
Events are a mechanism which allows the system to trigger a set of actions in response to actual events that happen on the system. When one of the users interfaces modifies the configuration databases, it must signal an event to regenerate the various server application configuration files according to the new configuration.
Note: The user interface must never modify configuration files directly. Neither should to the administrator from command line.
Each event is associated with a list of actions which should be
performed when the event occurs and is defined as a subdirectory of
/etc/e-smith/events/ containing symbolic links to the appropriate
actions, loosely modelled after the ‘’System V init’‘mechanism for
starting servers. For example, if you examine the
[root@nsrv actions]# ll /etc/e-smith/events/interface-update/ total 8 lrwxrwxrwx. 1 root root 34 Feb 6 11:19 S04interface-config-adjust -> ../actions/interface-config-adjust lrwxrwxrwx. 1 root root 33 Feb 6 11:19 S25interface-config-reset -> ../actions/interface-config-reset lrwxrwxrwx. 1 root root 33 Feb 6 11:19 S30interface-config-write -> ../actions/interface-config-write lrwxrwxrwx. 1 root root 35 Feb 6 11:19 S70interface-config-restart -> ../actions/interface-config-restart lrwxrwxrwx. 1 root root 36 Feb 6 11:19 S75interface-config-hostname -> ../actions/interface-config-hostname drwxr-xr-x. 2 root root 4096 Feb 6 11:20 services2adjust drwxr-xr-x. 3 root root 4096 Dec 18 11:17 templates2expand
The symbolic links are given prefixes such as S15, S85, etc. to specify
the order in which the actions should be executed in a similar manner to
the System V init mechanism.
You can change the actions performed by an event by changing the links
in the event directory. You can also create a new event by creating
another subdirectory of
Most events contain two common tasks: expanding various templates and
adjusting (e.g. restarting) the relevant services. For this reason, two
implicit actions are included in all events. These implicit actions mean
that additional code does not need to be written to perform these common
tasks. The implicit actions are represented by entries in the
services2adjust/ directory contains links mapping a specific
service to the action to perform on that service. For example, if
signalling the event in question requires that the ntpd service is
restarted, you simply include the link ntpd -> restart in the
services2adjust directory. The implicit action services2adjust would
then restart the ntpd service. As an example, the
directory for the
nethserver-httpd-update event is shown below:
# ls> l /etc/e-smith/events/nethserver-httpd-update/services2adjust/ total 0 lrwxrwxrwx. 1 root root 7 Oct 2 09:05 httpd -> restart
templates2expand/ directory contains a list of the configuration
files which need to be regenerated from their templates. This list
consists of a collection of empty files with the same file name as the
configuration file to be expanded and in a heirarchy mirroring their
location on the system. For example, to expand templates for the
/etc/samba/smb.conf configuration file, simply include the empty
etc/samba/smb.conf in the
templates2expand/ directory of
the relevant event.
Order of implicit actions¶
The implicit actions are implemented by inserting the action script
generic_template_expand early in the list of actions to be run in an
event and the
adjust-services action near the end of the list.
You should normally link your action scripts in the range S10 to S80 so
that they occur after templates2expand and before services2adjust.
generic_template_expand action is currently run at
adjust-services is run at S90.
signal-event program takes an event name as an argument, and
executes all of the actions in that event, providing the event name as
the first parameter and directing all output to the system log. It works
by listing the entries in the event directory and executing them in
sequence. So for example, the command:
will perform all the actions associated with the
event, which is defined by the contents of the
Events with arguments¶
So far we have described the following general principle throughout the system; changes are made by altering the database values, then signalling events. The actions triggered by each event typically regenerate entire configuration files, taking into account the latest configuration information.
However, some changes are best made incrementally. For example, consider
the user-create event. One of its actions updates the LDAP directory,
which it could do by deleting all of the users and recreating them based
on the updated
accounts database. However, this is inefficient and
would lose any additional LDAP attributes which may have been stored. It
would be better to simply add the new user incrementally, using the
default LDAP schema.
But how is the action code to know which user was just added? The new
username is passed as an argument to the user-create event. This way the
action programs triggered by the user-create event have a choice. They
can either ignore the username argument and regenerate their output
based on the updated list of accounts, or they can pay attention to the
username argument, retrieve the rest of the information about the new
user from the
accounts database, and perform the incremental work to
add the user.
Action scripts should normally take at most two arguments. The first is always the event name. The second optional argument is a key into one of the databases.
Events are not currently serialized. In most cases overlapping events will not cause issues, but caution should be exercised when events are signalled from programs.
Standard events and their arguments¶
The table below summarises the key NethServer events and their argument if required. Remember, each action script is always called with the event name as the first argument. The arguments listed in this table are provided as the second argument.
|certificate-update||The server public key certificate has been updated|
|fstab-update||Update /etc/fstab according fo fstab key and remount all fileystems|
|group-create||Group key||Called when a group is created|
|group-delete||Group key||Called when a group is deleted|
|group-modify||Group key||Called when a group is modified|
|group-create-pseudonyms||Signalled when the automatic creation of group email address is required|
|host-create||Host key||Called when a host is created|
|host-delete||Host key||Called when a host is deleted|
|host-modify||Host key||Called when a host is modified|
|hostname-modify||Called when the SystemName or DomainName keys have been modified|
|ibay-create||Shared folder key||Called when a shared folder is created|
|ibay-delete||Shared folder key||Called when a shared folder is deleted|
|ibay-modify||Shared folder key||Called when a shared folder is modified|
|interface-update||Called when a network interface configuration is updated in networks db|
|logrotate-update||Change default log retention and rotation policies|
|trusted-networks-update||The set of trusted networks is changed|
|migration-import||Path to migration directory||Import migration data from the given directory|
|password-expired||Username, expire date||The given username password will expire on expiredate|
|password-modify||User key||Called when a user password is modified|
|password-policy-update||User key||Called when the system password policy has been changed|
|post-backup-config||Called after configuration backup end|
|post-backup-data||Called after data backup end|
|post-restore-config||Called after restore of configuration|
|post-restore-data||Called after restore of data|
|pre-backup-config||The pre-backup-config event creates consistent system state for the backup|
|pre-backup-data||The pre-backup-data event creates consistent system state for the backup|
|pre-restore-config||Called before restore of configuration|
|pre-restore-data||Called before restore of data|
|pseudonym-create||Pseudonym key||Called when a pseudonym is created|
|pseudonym-delete||Pseudonym key||Called when a pseudonym is deleted|
|pseudonym-modify||Pseudonym key||Called when a pseudonym is modified|
|user-create||User key||Called when a user is created|
|user-delete||User key||Called when a user is deleted|
|user-modify||User key||Called when a user is modified|
|user-create-pseudonyms||User key||Called when the automatic creation of user’s email address(es) is required|
|user-lock||User key||Called when a user account is locked|
|user-unlock||User key||Called when a user account is unlocked|
|system-initialization||Initialize all system after installation|
When adding a user, the user is created in the
and various actions, such as creating the Linux account, are performed
user-create event. However, when deleting a user, we want to
accounts database entry for as long as possible, in
case there is information which the actions in the
might need in order to cleanly delete the users.
The system convention for handling deletions is:
- Change the type of the entry to mark it as being in the process of being deleted e.g. a’‘user’‘entry becomes a’‘user-deleted’‘entry.
- Signal the relevant deletion event - e.g.’‘user-delete’‘
- Remove the entry from the database, but only if the event succeeds. With this approach, the action scripts can decide whether to ignore the’‘user-deleted’’ entries when performing their tasks.
Output of event logs will be soon refactored!
All events, and all actions run by the event, are logged to the
messages system log. Here is an example action log, which has been
formatted onto multiple lines to enhance readability:
Feb 2 13:22:33 gsxdev1 esmith::event: S65sshd-conf=action| Event|remoteaccess-update| Action|S65sshd-conf| Start|1138846952 730480| End|1138846953 66768| Elapsed|0.336288
From this single log, we can see the action script name, which event it was called in, when it started, ended and how long it took (0.34 seconds). Now, let’s add an action script which always fails and signal the event again:
Feb 2 16:11:54 gsxdev1 esmith::event: S99false=action| Event|remoteaccess-update| Action|S99false| Start|1138857114 58910| End|1138857114 81920| Elapsed|0.02301| Status|256
Note that this log has a new field Status, which is added if the action script returns a false (non-zero) exit status. Suppressing the Status field when it is zero (success) makes it much easier to find failed actions in the logs.
If an action script fails, the entire event fails. The other actions scripts in the event are run, but the whole event is marked as having failed.
System validators provide an extensible UI-independent data validation layer.
On one hand UI implements fast grammar and/or syntax checks on input data. On the other, the system validators performs in-depth system consistency checks.
Validators have a behaviour very similar to events.
- A validator is a directory inside
- Each validator directory has a descriptive name, eg. user-name for a validator which validate a new user name.
- A validator is composed by an arbitrary number of actions saved inside
/etc/e-smith/validators/actionsdirectory and linked inside validator directory.
- A success validation occurs when all scripts return 0 (success validation) or at least one script returns 2 (sufficient valid condition).
A validator action are always called with a single parameter which is the value to be validated. Actions must return one of these exit values:
- 0: successful validation
- 1: validation failed
- 2: sufficient validation
- other value: specific error state
When a script returns 2 (sufficient validation) no further script will be processed.
Inside nethserver-devtools package there is
validator_actions() function which help creating links to actions just like
event_actions function. See
perldoc esmith::Build::CreateLinks for details.
Invoking a validator:
validate <validator-name> <value-to-validate>
validate user-name goofy